Optical device

An optical device comprising:

• a reflecting mirror including
• a reflecting surface to reflect light, and
• a supported portion disposed on a rear surface and having three supported surfaces arranged with rotational symmetry of 120 degrees around an optical axis, the rear surface being a surface of the reflecting mirror existing on the contrary side to the reflecting surface, the three supported surfaces being flat surfaces parallel to the optical axis;
• a structural member provided on a rear side of the reflecting mirror;
• and
• three supporting members, each of the three supporting members including mirror supporting portion connected to and supporting each of the three supported surfaces, having two ends connected to the structural member.

An optical device comprising:

• a reflecting mirror including
• a reflecting surface to reflect light, and
• a supported portion disposed on a rear surface and having three supported surfaces arranged with rotational symmetry of 120 degrees around an optical axis, the rear surface being a surface of the reflecting mirror existing on the contrary side to the reflecting surface;
• a structural member provided on a rear side of the reflecting mirror, the structural member having a hole in which the supported portion is contained;
• and
• three supporting members, each of the three supporting members including a mirror supporting portion connected to and supporting each of the three supported surfaces, and having two ends connected to the structural member.

An optical device comprising:

• a reflecting mirror including
• a reflecting surface to reflect light, and
• a supported portion disposed on a rear surface and having three supported surfaces arranged with rotational symmetry of 120 degrees around an optical axis, the rear surface being a surface of the reflecting mirror existing on the contrary side to the reflecting surface;
• a structural member provided on a rear side of the reflecting mirror, the structural member being formed of a honeycomb sandwich panel, the honeycomb sandwich panel including:
• a first skin being a plate material made of a low expansion metal, the low expansion metal being a metal having an absolute value of thermal expansion coefficient smaller than an absolute value of thermal expansion coefficient of carbon fiber reinforced plastic;
• a second skin being a plate material made of the low expansion metal and arranged to face the first skin;
• and a core made of carbon fiber reinforced plastic or the low expansion metal, the core being bonded to the first skin and the second skin and including a plurality of tubular cells each having a hexagonal cross section, the plurality of tubular cells being formed adjacently to each other;
• and
• three supporting members, each of the three supporting members including a mirror supporting portion connected to and supporting each of the three supported surfaces, having two ends connected to the structural member, the three supporting members being made of the low expansion metal.